In 2007, Koufos finished second to Buckeye teammate Jon Diebler in the Mr. Ohio Basketball voting. During his senior season with GlenOak, Koufos was named the Division I player of the year and was first-team all-state. He also earned first-team Northeast Inland all-district honors.
The 2007 McDonald’s and EA Sports All-American, Koufos averaged 25.9 points, 15.4 rebounds and 5.2 blocks per game. He was instrumental in GlenOak snapping Canton McKinley’s 41-game win streak in January of 2007 when he posted 32 points, 19 rebounds and 10 blocks to help the Golden Eagles edge the Bulldogs, 56-55, in overtime. The next day, Koufos recorded 32 points, 15 rebounds and seven blocks against Detroit Country Day, the No. 2 team in the state of Michigan, to lead GlenOak to its ninth-consecutive victory.
As a junior, Koufos averaged 24 points, 11.1 rebounds and four blocks per game and was named second-team all-state.
In April of 2007, Koufos was a member of the Royal team in the Jordan All-American Classic in Madison Square Garden.
During the summer of 2007, he participated in the Under-18 European championships in Madrid, Spain, for the Greek team. He was named the tournament MVP. He averaged 26.5 points, 13 rebounds and 3.5 blocked shots. Koufos led the national team to the finals against Serbia and in the championship recorded 33 points and 13 rebounds to lead Greece to the silver medal. In the semifinal game vs. Lithuania, he recorded 37 points, 20 rebounds and five blocks.
He is the son of Katerina and the late Alex Koufos. Kosta has one brother, Vasilios and a sister Maria. After graduation, Kosta plans to work in the business world or play professionally.